Chronic or persistent pain is influenced by the regulation of emotion. In particular, theory, anecdote, and empirical research suggest that suppressing or inhibiting anger is maladaptive for people with chronic pain. One line of research shows that suppressing the thoughts, feelings and behaviors associated with anger leads to increases in perceived pain severity, pain behavior, and muscle tension. A second line of research suggests the value of expressing or disclosing emotions for people with chronic pain. These two literatures have independently addressed two sides of the emotion regulation coin, and the proposed project will integrate these suppression and expression components into a single study. We propose that suppression of anger during an anger-inducing event exacerbates pain, but that the expression of inhibited anger can reverse this detrimental effect. A laboratory study of 360 patients with chronic low back pain (CLBP) -- a widespread and costly affliction - is proposed. Patients will be randomized to either suppress their thoughts, feelings, and behaviors (suppression condition) or to not suppress (control condition) while exposed to an anger-induction protocol. Subsequently, patients will be randomized to 1 of 2 active expression conditions (interpersonal expression vs. private expression) or to a no expression (control) condition. Finally, all patients will undergo a pain behavior task designed to provoke mild low back pain. This fully crossed design will allow us to test effects of anger suppression on later pain, to examine whether these effects can be reversed by anger expression, and to test whether interpersonal verbal expression is more effective than private expression. We will also test whether the degree of anger (vs. denial) expressed during verbal expression and reactivity of lower paraspinal muscles mediate effects of suppression and expression conditions, and whether gender, trait anger regulation style, alexithymia, and trauma history moderate effects of condition. We expect that anger suppression will lead to greater reports and displays of pain than not suppressing, but that patients allowed to verbally express following suppression will show evidence that the detrimental effects of suppression have been avoided or reversed. Results of this research will help clarify the implications of suppressing and/or expressing anger for adjustment among chronic pain patients. The findings also will provide an impetus to pursue therapeutic treatments for problematic anger regulation, and will help inform how to assess and intervene with anger, which is commonly experienced by patients suffering from a variety of painful medical conditions. Moreover, results will reveal specific pathways by which suppressed anger causes pain, and expressed anger alleviates it, that may then constitute empirically-supported targets for therapeutic interventions. Overall, this research contributes to our long-term objective, which is to guide the development of empirically-supported assessment and intervention procedures to improve emotion regulation in chronic pain, thereby decreasing the tremendous social and personal burden of chronic pain and disability.